Apparatus and method for fabricating bonded substrate

ABSTRACT

A bonded-substrate fabricating apparatus capable of reducing defective bonded substrates fabricated. A transfer robot sucks the outer edge area of the bottom surface of a substrate and spouts gas toward the bottom surface of the substrate to carry the substrate into a vacuum process chamber of a press machine while keeping the substrate horizontally. A press plate holds the substrate, which is held by the transfer robot, by suction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/347,625,filed Jan. 22, 2003, now U.S. Pat. No. 7,137,427.

This application is based upon and claims the priority of Japaneseapplication no. 2002-076173, filed Mar. 19, 2002, and U.S. patentapplication Ser. No. 10/347,625, filed Jan. 22, 2003, the contents beingincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus and method for fabricatingbonded substrate (panel). More particularly, the present inventionrelates to an apparatus and method for fabricating bonded substrate fora liquid crystal display (LCD), which is provided by bonding twosubstrates at a predetermined gap.

Nowadays, there are demands for large and thin liquid crystal display(LCD) panels capable of providing fine display on a large display area,and apparatus which fabricates such LCD panels have been developed. AnLCD panel is fabricated by arranging two glass substrates to face eachother at an extremely narrow gap (several micrometers) and filling aliquid crystal between the two glass substrates. The two glasssubstrates are, for example, an array substrate on which a plurality ofTFTs (Thin Film Transistors) are formed in a matrix form and a colorfilter substrate on which color filters (red, green and blue), a lightshielding film, etc. are formed. The light shielding film contributes toimproving contrast and shields light toward the TFTs to preventgeneration of an optical leak current. The array substrate is bonded tothe color filter substrate by a sealing material (adhesive) containing athermosetting resin.

A method of fabricating an LCD panel includes a liquid crystal sealingstep of sealing a liquid crystal between two glass substrates. Theconventional liquid crystal sealing step is carried out by the followingvacuum injection method. First, the TFT-formed array substrate is bondedto the color filter substrate (opposing substrate) via a sealingmaterial. The sealing material is cured. The bonded substrates and aliquid crystal are placed in a vacuum tank and an inlet port provided inthe sealing material is dipped in the liquid crystal. The pressure inthe tank is set back to the atmospheric pressure so that the liquidcrystal is sucked from the inlet port. Finally, the inlet port of thesealing material is sealed.

Recently, attention has been paid to the following dropping methodinstead of the vacuum injection method. First, the frame of a sealingmaterial is formed in such a way as to enclose the outer periphery ofthe array substrate. A predetermined dose of a liquid crystal is droppedon the surface of the array substrate within the frame of the sealingmaterial. Finally, the array substrate is bonded to the color filtersubstrate in vacuum. The dropping method can reduce the amount of aliquid crystal in use significantly and can shorten the time needed forthe liquid crystal sealing step, thus resulting in a reduction in panelfabrication cost. It is therefore expected that mass production will beimproved.

A bonded-substrate fabricating apparatus which operates according to thedropping method has the following problems.

1. Improper Chuck Originated from the Bending of Substrate

Normally, a substrate is held by suction by vacuum chuck or chucking byelectrostatic chuck. In the vacuum-chuck holding, a holding plate whichcan hold a substrate by vacuum suction is used. The array substrate isheld by the holding plate and the frame of the sealing material isformed on the array substrate. The adequate amount of a liquid crystalis dropped on the surface of the array substrate from a dispenser.Finally, the array substrate is bonded to the color filter substrate ina vacuum atmosphere.

In the electrostatic-chuck holding, a holding plate which has anelectrode is used. A voltage is applied between the electrode of theholding plate and a conductive film formed on a glass substrate togenerate Coulomb's force between the glass and the electrode. TheCoulomb's force electrostatically holds the glass substrate on theholding plate.

In the vacuum-chuck holding, when the degree of vacuum in the processchamber becomes as high as a certain level, vacuum chuck does not work.In this respect, the substrate is electrostatically held byelectrostatic chuck before suction by vacuum chuck stops working.

Normally, two substrates are separately held by an upper holding plateand a lower holding plate and are bonded together. Specifically, toprevent transfer of dust on the bonded surfaces or contaminationthereof, the outer edge areas (portions outward of the frame of thesealing material) of the substrates are held by a transfer robot and aremoved into the process chamber. However, the large and thin substratesare likely to curve (bend) due to their dead loads. The holding platescannot stably hold the bent substrates. If the process chamber isdepressurized for the purpose of bonding the substrates, therefore, themisalignment of the substrates or separation of the substrates from theholding plates may occur.

In a case where the holding plate (electrostatic chuck)electrostatically holds a bent substrate, glow discharge occurs duringdepressurization of the process chamber. This case brings about aproblem such that a circuit or TFT devices formed on the substrate aredamaged, resulting in generation of defects. In addition, as air remainsbetween the holding plate and the substrate, the substrate may bereleased from the electrostatic chuck while depressurizing the processchamber.

2. Improper Bonding Originated from the Bending of Substrate

In the bonding step, two substrates are pressed while keeping apredetermined substrate gap. The important factors in the bonding stepare to keep the two substrates parallel to each other and to press thetwo substrates with a uniform load. If the substrates are bent, however,the frame of the sealing material is pressed unevenly in the bondingstep, so that the liquid crystal may be pushed out of the frame of thesealing material. If the pressing pressure is uneven, the pressingpressure needed to seal the liquid crystal increases so that theinfluence on the substrates becomes greater. This makes it difficult tofabricate stable products.

3. Dust Oriented Improper Chuck

The holding plates that hold the two substrates separately have chucksurfaces which are planarized at a high precision. In a case where dustor glass pieces are adhered to the chuck surfaces, the dust istransferred onto the substrates, causing the misalignment of thesubstrates or separation of the substrates from the holding plates. Asminute dust is adhered to the holding plates by electrostatic force,however, it is difficult to remove the dust from the holding plates.

4. Defects Originated from Variation in Cell Thickness

It is necessary to properly adjust the amount of a liquid crystal to besealed in an extremely narrow substrate gap (cell thickness). The gapbetween the two substrates is determined by placing spacers between thesubstrates or forming poles on one of the substrates. However, thespacers and poles have a slight height variation. This results in achange in the substrate gap, so that the amount of the liquid crystalsealed may become too much or too little locally. This would bring abouta problem such that the cell thickness would vary after the substrateswere bonded. The variation in cell thickness cause uneven display of theLCD panel.

SUMMARY OF THE INVENTION

Accordingly, it is an objective of the present invention to provide abonded-substrate fabricating apparatus and fabricating method which cansuppress fabrication of defective bonded substrates.

To achieve the above object, the present invention provides an apparatusfor fabricating a bonded substrate by bonding a first substrate and asecond substrate, each of the first substrate and the second substratehaving an inner surface to be bonded and an outer surface opposite tothe inner surface. The apparatus includes a first holding plate forholding the first substrate, a second holding plate arranged to face thefirst holding plate for holding the second substrate by chucking theouter surface of the second holding plate, and a transfer machine whichtransfers the first and second substrates to the first and secondholding plates respectively and includes a holding member for holdingthe second substrate horizontally by chucking the second substrate andspouting gas onto the inner surface of the second substrate.

A further perspective of the present invention is an apparatus forfabricating a bonded substrate by bonding a first substrate and a secondsubstrate, each of the first substrate and the second substrate havingan inner surface to be bonded and an outer surface opposite to the innersurface. The apparatus includes a first holding plate for holding thefirst substrate by chucking the outer surface of the first holdingplate, a second holding plate arranged to face the first holding platefor holding the second substrate by chucking the outer surface of thesecond holding plate, and a transfer machine which transfers the firstand second substrates to the first and second holding platesrespectively and includes a holding member for holding the first andsecond substrates by chucking the outer surfaces of the first and secondsubstrates.

A further perspective of the present invention is an apparatus forfabricating a bonded substrate by bonding a first substrate and a secondsubstrate, each of the first substrate and the second substrate havingan inner surface to be bonded and an outer surface opposite to the innersurface. The apparatus includes a transfer machine which transfers thefirst and second substrates and includes a holding member for holdingthe first and second substrates by chucking the outer surfaces of thefirst and second substrates, a first holding plate for holding the firstsubstrate transferred by the transfer machine, and a second holdingplate arranged to face the first holding plate for holding the secondsubstrate transferred by the transfer machine. At least one of the firstand second holding plates has a channel for retaining the associatedholding member when transfer of the associated holding member from thetransfer machine is executed.

A further perspective of the present invention is an apparatus forfabricating a bonded substrate by bonding a first substrate and a secondsubstrate. The apparatus includes a transfer machine which transfers thefirst and second substrates and includes a plurality of holding membersfor holding the first and second substrates horizontally, a firstholding plate having a chuck surface for chucking the first substratetransferred by the transfer machine, and a second holding plate arrangedto face the first holding plate and having a chuck surface for chuckingthe second substrate transferred by the transfer machine. At least oneof the first and second holding plates includes a chuck mechanism whichis movable up and down independently of the associated chuck surface andsucks and holds the associated substrate. The associated chuck surfaceholds the associated substrate held by the chuck mechanism by at leastone of suction and electrostatic force.

A further perspective of the present invention is a method offabricating a bonded substrate by bonding two substrates in a processchamber. The method includes sucking at least one substrate and causinga holding plate to hold that substrate under an atmospheric pressure,depressurizing the process chamber, stopping suction of the at least onesubstrate to make a back pressure of the at least one substrateapproximately equal to a pressure in the process chamber, and causingthe at least one substrate to be electrostatically held by the holdingplate.

A further perspective of the present invention is a method offabricating a bonded substrate by bonding two substrates in a processchamber. The method includes sucking at least one substrate and causinga holding plate to hold that substrate under an atmospheric pressure,depressurizing the process chamber, changing a pressure in the processchamber to a value higher than the atmospheric pressure by apredetermined pressure, and stopping suction of the at least onesubstrate to electrostatically hold that substrate.

Other aspects and advantages of the present invention will becomeapparent from the following description, taken in conjunction with theaccompanying drawings, illustrating by way of example the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel areset forth with particularity in the appended claims. The invention,together with objects and advantages thereof, may best be understood byreference to the following description of the presently preferredembodiments together with the accompanying drawings in which:

FIG. 1 is a block diagram of a bonded-substrate fabricating apparatusaccording to the present invention;

FIG. 2 is a schematic diagram of the chuck mechanism of a press machineaccording to a first embodiment of the present invention;

FIG. 3 shows the chuck mechanism of the press machine in FIG. 2;

FIGS. 4A, 4B and 4C show the chuck surface of a press plate;

FIG. 5 is a flowchart of a bonding method;

FIG. 6 is a flowchart of another bonding method;

FIG. 7A is an enlarged view of a locally bent substrate;

FIG. 7B is an enlarged view of a substrate whose local bending isprevented;

FIG. 8 is a diagram for explaining elimination of an impurity by usingan adhesive sheet;

FIG. 9 shows bonded substrates between which a liquid crystal is sealed;

FIG. 10 is a block diagram of a control method for the amount of theliquid crystal;

FIGS. 11A and 11B are flowcharts of the control method for the amount ofthe liquid crystal;

FIG. 12 shows the layout of a transfer robot according to a secondembodiment of the present invention;

FIG. 13A is a schematic diagram of the transfer robot in FIG. 12;

FIGS. 13B and 13C are enlarged views of hands of the transfer robot inFIG. 12;

FIG. 14A is a plan view of a positioning device in FIG. 12;

FIG. 14B is a side view of the positioning device in FIG. 14A;

FIGS. 15A and 15B show a press plate according to the second embodiment;

FIG. 16 is a schematic diagram of the chuck mechanism of a press machineaccording to a third embodiment of the present invention;

FIG. 17 is a flowchart of a bonding method which is executed by thepress machine in FIG. 16; and

FIGS. 18A and 18B show the chuck mechanism of a press plate according toa fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A bonded-substrate fabricating apparatus 10 according to the firstembodiment of the present invention will be described below.

The bonded-substrate fabricating apparatus 10 injects a liquid crystalbetween a first substrate W1 and a second substrate W2 and bonds thesubstrates W1 and W2 to fabricate a liquid crystal display. The liquidcrystal display is, for example, an active matrix type liquid crystaldisplay panel. The first substrate W1 is an array substrate (TFTsubstrate) of glass which has an array of TFTs, and the second substrateW2 is a color filter (CF) substrate which has color filters and a lightshielding film. The substrates W1 and W2 are fabricated separately andare supplied to the bonded-substrate fabricating apparatus 10.

As shown in FIG. 1, the bonded-substrate fabricating apparatus 10includes a control unit 11, a seal patterning system 12, a liquidcrystal dropping device 13 and a bonding device 14. The bonding device14 comprises a press machine 15 and a curing device 16. The control unit11 controls the seal patterning system 12, the liquid crystal droppingdevice 13 and the bonding device 14 (the press machine 15 and curingdevice 16). Each of the components 11 to 13, 15 and 16 is used in theplural as needed.

The bonded-substrate fabricating apparatus includes first to fifthtransfer equipments 17 a to 17 e which transfer the first substrate W1and the second substrate W2. The control unit 11 controls the first tofifth transfer equipments 17 a to 17 e and a transfer robot 31 (see FIG.2) provided in the bonding device 14 to transfer the first substrate W1and the second substrate W2 and an bonded substrate (integratedsubstrate).

The first transfer equipment 17 a transfers the first substrate W1 andthe second substrate W2 to the seal patterning system 12. The firsttransfer equipment 17 a has an ID reader 18 for reading identificationinformation (substrate ID) to distinguish the types of the firstsubstrate W1 and the second substrate W2. As the first substrate W1 andthe second substrate W2 are supplied to the first transfer equipment 17a, the ID reader 18 reads the substrate ID in response to a controlsignal from the control unit 11 and the first transfer equipment 17 atransfers the first substrate W1 and the second substrate W2 to the sealpatterning system 12. The control unit 11 controls the dropping amountof a liquid crystal based on the substrate ID.

The seal patterning system 12 receives the first substrate W1 and thesecond substrate W2 and applies a sealing material in predeterminedpositions on the top surface of one of the first substrate W1 and thesecond substrate W2 (the first substrate W1 in the first embodiment)along the periphery, thereby forming the frame of the sealing material.The sealing material is preferably an adhesive including a photocuringadhesive.

The second transfer equipment 17 b receives the first substrate W1 andthe second substrate W2 from the seal patterning system 12 and transfersthe first substrate W1 and the second substrate W2 as a set to theliquid crystal dropping device 13.

After the sealing material is applied, the liquid crystal droppingdevice 13 drops a liquid crystal at predetermined positions on the topsurface of the first substrate W1. After the dropping, the firstsubstrate W1 and the second substrate W2 are transferred to the bondingdevice 14 by the third transfer equipment 17 c.

The press machine 15 of the bonding device 14 is provided with apositioning device 102 (see FIG. 12). The first substrate W1 and thesecond substrate W2 are transferred to the positioning device 102. Thefirst substrate W1 and the second substrate W2 should be bonded afterbeing aligned accurately. Accordingly, the positioning device 102performs preliminary positioning of the first substrate W1 and thesecond substrate W2 before those substrates W1 and W2 are supplied tothe press machine 15. The positioned first substrate W1 and the secondsubstrate W2 are transferred to the press machine 15 by the transferrobot.

The press machine 15 has a vacuum process chamber 20 (see FIG. 3). Anupper chuck, or a press plate 24 a, for chucking the second substrate(upper substrate) W2 and a lower chuck, or a table 24 b, for chuckingthe first substrate (lower substrate) W1 are provided in the vacuumprocess chamber 20. The first substrate W1 and the second substrate W2are simultaneously transferred to the press machine 15 and areseparately held by the table 24 b and the press plate 24 a.

The press machine 15 evacuates the vacuum process chamber 20 and feeds apredetermined gas to the vacuum process chamber 20 to perform apreprocess on the substrates W1 and W2. The predetermined gas is asubstitution gas including a reactive gas, such as an exciting gas for aplasma display panel (PDP), an inactive gas, such as a nitrogen gas, orclean dry air. In the preprocess, impurities and products which areadhered to the surfaces of the substrates W1 and W2 or the surfaces ofdisplay elements is exposed to the predetermined gas for a predeterminedtime. The preprocess stably maintains the property of the bondedsurfaces which cannot be unsealed after bonding. In general, an oxidefilm is formed on the surfaces of the substrates W1 and W2 so that anairborne material in the air is adhered to the surfaces. This changesthe states of the surfaces of the substrates W1 and W2. As the degree ofa change in the surface state varies between the substrates W1 and W2,the qualities of the panels differ from one panel to another. In thisrespect, changes in the surfaces of the substrates W1 and W2 aresuppressed by performing the preprocess which suppresses the formationof a film and the adhesion of an impurity and processes the adheredimpurity.

The press machine 15 aligns the first substrate W1 with the secondsubstrate W2, while optically detecting an alignment mark, in such a waythat the sealing material and liquid crystal on the first substrate W1do not contact the bottom surface of the second substrate W2. The pressmachine 15 presses the substrates W1 and W2 with a predeterminedpressure in such a way as to ensure a predetermined cell thickness.After pressing, the press machine 15 releases the vacuum process chamber20 to set the pressure in the vacuum process chamber 20 to theatmospheric pressure.

While monitoring the time passed from the point when the substrates W1and W2 were transferred to the vacuum process chamber 20, the controlunit 11 controls the time from the point of transfer to the point ofbonding in such a way that the substrates W1 and W2 are exposed to thegas supplied to the vacuum process chamber 20 over a predetermined time.This stabilizes the bonded surfaces of the substrates W1 and W2 andallows the bonded surfaces to have a predetermined property.

The fourth transfer equipment 17 d removes the bonded substrate(integrated substrate W1, W2 or liquid crystal panel) from the pressmachine 15 and transfers it to the curing device 16. When the timepassed from the point at which the liquid crystal panel was pressedreaches a predetermined time, the control unit 11 drives the fourthtransfer equipment 17 d to supply the liquid crystal panel to the curingdevice 16.

The liquid crystal that has been sealed in the liquid crystal panelspreads between the substrates W1 and W2 by the pressing pressure andthe atmospheric pressure. It is necessary to cure the sealing materialbefore the liquid crystal reaches the frame of the sealing material.Therefore, the curing device 16 irradiates light having a predeterminedwavelength to the liquid crystal panel to cure the sealing materialafter a predetermined time passes after pressing. The predetermined timeis determined by acquiring the spreading time of the liquid crystal andthe time needed to release the press stress remaining on the substratesW1 and W2 beforehand through experiments.

The press stress remains on the integrated substrate W1, W2. Because thesealing material is not cured while the substrates W1 and W2 aretransferred to the fourth transfer equipment 17 d, the stress remainingon the substrates W1 and W2 is released. As the stress hardly remains onthe substrates W1 and W2 when the sealing material is cured, thegeneration of a positional deviation is reduced.

After the sealing material is cured, the fifth transfer equipment 17 etransfers the liquid crystal panel from the curing device 16 to a devicewhich executes the subsequent step. The subsequent step is, for example,an inspection step for inspecting the positional deviation between thefirst substrate W1 and the second substrate W2. The inspection result isfed back to the press machine 15 in order to correct the alignment ofsubstrates to be pressed next.

The press machine 15 will be discussed in detail below.

As shown in FIG. 2, the vacuum process chamber 20 is separated into anupper container 20 a and a lower container 20 b which are separable upand down.

The upper container 20 a is supported by a lift mechanism (not shown) insuch a way as to be movable up and down. As shown in FIG. 3, as theupper container 20 a is moved down, the vacuum process chamber 20 issealed tightly. A seal 21 provided at the top side of the lowercontainer 20 b seals between the upper container 20 a and the lowercontainer 20 b.

Provided in the vacuum process chamber 20 are an upper holding plate 22a and a lower holding plate 22 b which chuck the substrates W1 and W2,respectively. In the first embodiment, the second substrate W2 ischucked by the upper holding plate 22 a and the first substrate W1 bythe lower holding plate 22 b. The upper holding plate 22 a is supportedby a lift mechanism (not shown) in such a way as to be movable up anddown. The lower holding plate 22 b is supported by an unillustrateddrive mechanism in such a way as to be slidable along the horizontalplane (X axis and Y axis) and rotatable horizontally.

The upper holding plate 22 a has an upper surface plate 23 a, a pressplate 24 a or an electrostatic chuck portion mounted to the bottomsurface of the upper surface plate 23 a, and a vacuum line 25 for vacuumchucking of the second substrate W2. The vacuum line 25 includes aplurality of chuck holes opened in the bottom surface of the press plate24 a and a horizontal line communicated with the chuck holes and formedhorizontally in the upper surface plate 23 a.

The vacuum line 25 is connected to a first vacuum pump 27 via a mainpipe 26 a. The main pipe 26 a is provided with a chuck valve 28 a. Thefirst vacuum pump 27 and the chuck valve 28 a are connected to thecontrol unit 11. The control unit 11 controls the driving of the vacuumpump 27 and the opening/closing of the valve 28 a. An unillustratedpressure sensor is provided in the main pipe 26 a.

The main pipe 26 a is connected to a pipe 26 b having an opening in thebottom surface of the upper surface plate 23 a. The pipe 26 b isprovided with a back pressure release valve 28 b. The opening/closing ofthe valve 28 b is controlled by the control unit 11. As the valve 28 bis opened, the pressure in the vacuum line 25 is approximately equalizedto the pressure in the vacuum process chamber 20 and the back pressureof the second substrate W2.

The main pipe 26 a is connected to an atmosphere pipe 26 c. Theatmosphere pipe 26 c is provided with an atmosphere valve 28 c. Theopening/closing of the atmosphere valve 28 c is controlled by thecontrol unit 11. As the atmosphere valve 28 c is opened, the air is ledinto the main pipe 26 a via the atmosphere pipe 26 c, making the backpressure of the second substrate W2 approximately equal to theatmospheric pressure.

The lower holding plate 22 b has a lower surface plate 23 b and anelectrostatic chuck portion or the table 24 b mounted to the top surfaceof the lower surface plate 23 b. Although the lower holding plate 22 bis not provided with a suction mechanism for vacuum chucking of thesubstrate W1, the lower holding plate 22 b, like the upper holding plate22 a, may be provided with a chuck mechanism (pump 27, pipes 26 a, 26 band 26 c, and valves 28 a, 28 b and 28 c).

The lower container 20 b is connected via a depressurizing pipe 26 d toa second vacuum pump 29 for depressurizing the vacuum process chamber20. The depressurizing pipe 26 d is provided with an exhaust valve 28 d.The second vacuum pump 29 and the exhaust valve 28 d are controlled bythe control unit 11.

A gas pipe 26 e for feeding the predetermined gas to the vacuum processchamber 20 is connected to the upper container 20 a. The gas pipe 26 eis provided with a gas inlet valve 28 e whose opening/closing action iscontrolled by the control unit 11.

The control unit 11 drives the first vacuum pump 27 and opens the chuckvalve 28 a to evacuate the vacuum line 25 and the main pipe 26 a andvacuum-chuck the second substrate W2. The control unit 11electrostatically chucks the substrates W2 and W1 by Coulomb's forcegenerated by applying a voltage to the press plate 24 a and the table 24b.

The control unit 11 switches the chuck mode for the second substrate W2to vacuum chuck or electrostatic chuck in accordance with the pressure(degree of vacuum) in the vacuum process chamber 20. At the time thesecond substrate W2 is transferred to the vacuum process chamber 20, forexample, the control unit 11 causes the press plate 24 a to hold thesecond substrate W2 by vacuum chuck (pressure differential). When thepressure in the vacuum process chamber 20 becomes lower than thepressure in the main pipe 26 a (and the vacuum line 25), on the otherhand, the control unit 11 closes the chuck valve 28 a to disconnect thevacuum line 25 from the vacuum pump 27 and causes the press plate 24 ato hold the second substrate W2 by electrostatic force.

Next, a step of carrying the substrates W1 and W2 into the press machine15 will be discussed by referring to FIG. 2. In the followingdescription, the surfaces to be bonded, i.e., the surfaces that contactthe liquid crystal (the top surface of the first substrate W1 and thebottom surface of the second substrate W2) are called “inner surfaces”and the opposite surfaces (the bottom surface of the first substrate W1and the top surface of the second substrate W2) are called “outersurfaces”.

The second substrate W2 is vacuum-chucked by the transfer robot 31 andis carried into the press machine 15. The transfer robot 31 has aholding member including a mechanism to chuck the second substrate W2 ora hand 31 a.

The hand 31 a of the transfer robot 31 has a plurality of chuck pads 32for chucking the outer edge area of the inner surface of the secondsubstrate W2 (the portion between the frame of the sealing material andthe edge of the substrate). The chuck pads 32 are connected to anunillustrated vacuum source via a chuck line 33 formed in the hand 31 a.

The hand 31 a has at least one gas injection nozzle 34 provided in sucha way as to face a portion inward of the outer edge area of the innersurface of the second substrate W2. The gas injection nozzle 34 isconnected to a gas supply source (not shown) via a gas supply line 34 aformed in the hand 31 a and an unillustrated pipe, so that the gas fedfrom the gas supply source is injected toward the inner surface of thesecond substrate W2 from the gas injection nozzle 34.

The gas injection amount (flow rate) is set in such a way as to generatea pressure equivalent to the weight of the second substrate W2 per unitarea. The setting is carried out by first estimating the gas injectionamount based on the area, thickness and specific gravity of the secondsubstrate W2, the pitch between the gas injection nozzles 34 and thedistance between the nozzles 34 and the inner surface of the secondsubstrate W2, and then confirming the amount through experiments. As thebending of the second substrate W2 by the dead load is prevented by thegas injection pressure, the second substrate W2 is held by the transferrobot 31 in an approximately horizontal state.

The gas to be spouted on the second substrate W2 is, for example, theaforementioned reactive gas, nitrogen gas or dean dry air. As the innersurface of the second substrate W2 is exposed to such a gas, an impurityor product adhered to the second substrate W2 is removed.

The transfer robot 31 causes the second substrate W2 to approach thechuck surface of the press plate 24 a while keeping the second substrateW2 in a flat state. The press plate 24 a holds the second substrate W2by effecting at least one of suction and electrostatic force.

A description will now be given of the transfer of the substrate W1 (thesubstrate held on the table 24 b).

The substrate W1 is carried into the press machine 15 while beingchucked and held by another hand (not shown in FIG. 2) of the transferrobot 31.

The table 24 b is provided with known lift pins (not shown) that aresupported in a vertically movable manner. The substrate W1 transferredby the transfer robot 31 is received by a plurality of lift pinselevated, and is placed on the table 24 b as the lift pins are moveddownward. As electrostatic force is let to work on the substrate W1 fromthe table 24 b in that state, the substrate W1 is held on the table 24b.

The press plate 24 a will be discussed next.

As shown in FIG. 4B, a plurality of grooves 25 a are formed in the chucksurface of the press plate 24 a at predetermined pitches. With thesecond substrate W2 held by the press plate 24 a, the grooves 25 a donot communicate with the vacuum line 25. The grooves 25 a extend to theend face (side surface) of the press plate 24 a along a predetermineddirection (see FIGS. 4A and 4C).

Bubbles that remain between the press plate 24 a and the secondsubstrate W2 at the time of depressurizing the vacuum process chamber 20are moved into the vacuum process chamber 20 via the grooves 25 a. Thisprevents the bubbles from remaining between the press plate 24 a and thesecond substrate W2 at the time of depressurizing the vacuum processchamber 20 and thus prevents the second substrate W2 from moving andcoming off.

The grooves 25 a make the contact area between the chuck surface and thesecond substrate W2 smaller. When the stress stored on the secondsubstrate W2 is released, therefore, the position of the secondsubstrate W2 is prevented from being deviated.

Grooves similar to the grooves 25 a of the press plate 24 a are likewiseformed on chuck surface of the table 24 b. Therefore, the substrate W1is held in a flat state and in contact with the press plate 24 a, thuspreventing the movement and separation of the substrate W1.

Referring now to FIG. 5, a method of bonding the substrates W1 and W2will be discussed.

In step S41, the press machine 15 is initialized. That is, the valves 28a to 28 e are all closed and the upper container 20 a is moved upward toopen the vacuum process chamber 20. The first and second vacuum pumps 27and 29 normally driven.

In an unillustrated step, the frame of the sealing material (adhesive)is formed on the first substrate W1 beforehand and a liquid crystal isdropped on the surface of the first substrate W1 defined by the frame.The substrates W1 and W2 are transferred to the initialized pressmachine 15 by the transfer robot 31. Specifically, the transfer robot 31places the second substrate W2 close to the press plate 24 a whileholding the substrate W2 in an approximately horizontal state. In stepS42, the press machine 15 opens the chuck valve 28 a to allow the pressplate 24 a to hold the second substrate W2 by vacuum chuck. In step S43,the transfer robot 31 places the first substrate W1 onto the table 24 b.In step S43, the press machine 15 applies a predetermined voltage to thetable 24 b. This causes the substrate W1 to be electrostatically held onthe table 24 b.

In step S44, the press machine 15 lifts down the upper container 20 a ofthe vacuum process chamber 20 to close the vacuum process chamber 20. Instep S45, the press machine 15 opens the back pressure release valve 28b. This allows the vacuum line 25 and the main pipe 26 a to communicatewith the interior of the vacuum process chamber 20 via the pipe 26 b, sothat the back pressure of the second substrate W2 (the pressure in thevacuum line 25) becomes approximately equal to the pressure in thevacuum process chamber 20 (chamber pressure). That is, the pressure onthe inner surface side of the second substrate W2 becomes approximatelyequal to the pressure on the outer surface side. This prevents thesecond substrate W2 from locally bent by the pressure differentialbetween the top and bottom surfaces of the second substrate W2, so thatthe second substrate W2 can be stably held on the press plate 24 a in anapproximately flat state.

In step S46, the press machine 15 closes the chuck valve 28 a. Whilethis releases the suction force acting on the second substrate W2, thesecond substrate W2 does not come off the press plate 24 a soon. This isbecause the outer surface of the second substrate W2 and the chucksurface of the press plate 24 a are almost flat and moisture containedin the air is intervened between the press plate 24 a and the secondsubstrate W2, so that adhesion strength remains between the press plate24 a and the second substrate W2. In step S47, the press machine 15applies a voltage to the press plate 24 a to electrostatically chuck thesecond substrate W2 within a period during which the second substrate W2is held on the press plate 24 a by the adhesion strength.

In step S48, the press machine 15 opens the exhaust valve 28 d and thegas inlet valve 28 e. As a result, substitution with an inactive gas iscarried out while the vacuum process chamber 20 is depressurized by thevacuum pump 29. Because the second substrate W2 is electrostaticallychucked to the press plate 24 a in an approximately flat state duringdepressurization of the vacuum process chamber 20, bubbles hardly remainon the contact surface between the second substrate W2 and the pressplate 24 a. This suppresses the generation of a glow discharge, thuspreventing the positional deviation and separation of the secondsubstrate W2.

After a predetermined time elapses, gas substitution in the vacuumprocess chamber 20 is completed. In step S49, the press machine 15closes the gas inlet valve 28 e after the gas substitution is completed.In step S50, the press machine 15 optically detects an alignment markand aligns the first and second substrates W1 and W2 with each other insuch a way that the sealing material on the substrate W1 and the liquidcrystal do not contact the bottom surface of the substrate W2.

In step S51, the press machine 15 lifts down the upper surface plate 23a and applies a predetermined pressure to the substrates W1 and W2 topress the substrates W1 and W2 to a predetermined cell thickness andbond the substrates W1 and W2 together in vacuum.

After bonding of the substrates W1 and W2, the press machine 15 stopselectrostatic chuck of the press plate 24 a in step S52. In step S53,the press machine 15 closes the exhaust valve 28 d to open theatmosphere valve 28 c. As a result, the pressure in the vacuum processchamber 20 becomes the atmospheric pressure.

In step S54, the press machine 15 stops electrostatic chuck of the table24 b and lifts the upper surface plate 23 a upward. The integratedsubstrate W1, W2 remains on the table 24 b. The press machine 15 movesthe upper container 20 a to the upper end to open the vacuum processchamber 20.

In step S55, the transfer robot 31 removes the integrated substrate W1,W2 from the table 24 b and transfers it to the device that executes thesubsequent step. In step S56, the process returns to step S41.

As the local bending of the second substrate W2 is corrected and thesecond substrate W2 is held on the press plate 24 a in an approximatelyflat state by the electrostatic force according to the bonding method inFIG. 5, the positional deviation and separation of the second substrateW2 are prevented during depressurization of the vacuum process chamber20.

The bonding method in FIG. 5 may be modified as illustrated in FIG. 6.

Steps S61 to S64 in FIG. 6 are the same as steps S41 to S44 in FIG. 5.That is, after initialization of the press machine 15, the secondsubstrate W2 is held on the press plate 24 a, the substrate W1 is heldon the table 24 b and the vacuum process chamber 20 is closed.

In step S65, the press machine 15 opens the gas inlet valve 28 e to letthe gas enter the vacuum process chamber 20. This raises the chamberpressure to, for example, the atmospheric pressure+2 kPa (kilo pascals).

The press machine 15 stops evacuation of the vacuum process chamber 20by closing the chuck valve 28 a (step S66) and opens the atmospherevalve 28 c to set the pressures in the main pipe 26 a and vacuum line 25to the atmospheric pressure (step S67).

At this time, as the gas inlet valve 28 e is open, the gas is fed intothe vacuum process chamber 20 so that the chamber pressure is higherthan the atmospheric pressure. Therefore, the second substrate W2 isheld on the press plate 24 a by the pressure differential between thechamber pressure and the atmospheric pressure. The pressure differentialis controlled in such a way as to become a level which is sufficient tohold the second substrate W2 on the press plate 24 a (e.g., the chamberpressure=atmospheric pressure+2 kPa). Accordingly, the local bending ofthe second substrate W2 is suppressed so that the second substrate W2 isstably fixed on the press plate 24 a in an approximately flat state.

The press machine 15 applies a voltage to the press plate 24 a to allowthe press plate 24 a to electrostatically hold the second substrate W2(step S68) and closes the atmosphere valve 28 c and the gas inlet valve28 e to open the back pressure release valve 28 b (step S69). Openingthe back pressure release valve 28 b eliminates the pressuredifferential between the top and bottom surfaces of the second substrateW2, thus preventing the occurrence of local bending of the secondsubstrate W2 and the positional deviation and separation of the secondsubstrate W2.

In step S70, the press machine 15 opens the exhaust valve 28 d and thegas inlet valve 28 e. Consequently, the vacuum process chamber 20 isevacuated by the vacuum pump 29 and gas substitution is carried out. Atthis time, the second substrate W2 is electrostatically chucked to thepress plate 24 a in an approximately flat state and bubbles hardlyremain on the contact surface of the second substrate W2 and the pressplate 24 a. This suppresses the generation of a glow discharge, thuspreventing the positional deviation and separation of the secondsubstrate W2.

In step S71, the press machine 15 closes the gas inlet valve 28 e aftergas substitution in the vacuum process chamber 20 is completed. StepsS72 to S78 are the same as steps S50 to S55 in FIG. 5.

According to the bonding method in FIG. 6, bending of the secondsubstrate W2 is prevented and positional deviation and separation of thesecond substrate W2 are prevented in a period during which the vacuumprocess chamber 20 is evacuated. While the vacuum chuck of the secondsubstrate W2 is stopped and the second substrate W2 is electrostaticallyheld, the second substrate W2 is pressed on the press plate 24 a andstably held by the pressure differential originated from the supply ofthe gas. Further, the method allows the gas to efficiently removeimpurities in the vacuum process chamber 20 and on the inner surface ofthe second substrate W2.

A description will now be given of local bending of the second substrateW2.

When the press plate 24 a holds the second substrate W2 by suction,local bending occurs as shown in FIG. 7A due to the pressuredifferential between the top and bottom surfaces of the second substrateW2. The thinner the second substrate W2 is, the more prominent thebending originated from the pressure differential becomes.

To prevent local bending, it is preferable to provide a porous member 80of porous ceramics or the like which has, for example, a permeability inthe grooves 25 a. Providing the porous member 80 in the grooves 25 aimproves the rigidity of the chuck surface and makes the chuck surfaceflat, thus preventing local bending of the second substrate W2. In thebonding step of the substrates W1 and W2, the effect of preventingpositional deviation and separation of the second substrate W2 from thepress plate 24 a due to the bending of the second substrate W2 isfurther improved.

To prevent a waste from being stored inside the porous member 80 andcontaminating the second substrate W2, it is desirable to eliminate dustor the like by regular counterflow of a gas (inactive gas).

A description will now be given of a method of removing impurities fromthe press plate 24 a and table 24 b.

Impurities, such as dust or glass pieces of the substrates W1 and W2,are apt to be adhered to the press plate 24 a and the table 24 b. Theimpurities may damage the chuck surfaces of the press plate 24 a andtable 24 b or may cause positional deviation and separation of thesubstrates W1 and W2 at the time of chucking the substrates W1 and W2.It is therefore necessary to eliminate the impurities adhered to thepress plate 24 a and table 24 b.

FIG. 8 shows an adhesive sheet 81 which comprises a tape base 82 and anadhesive layer 83 formed by applying an adhesive to both sides of thetape base 82. Impurities 84, such as dust or glass pieces, adhered tothe press plate 24 a and table 24 b are removed by using the adhesivesheet 81. Specifically, first, an impurity eliminating device (sheetfeeder) 800 feeds the adhesive sheet 81 into the press machine 15 andadheres the adhesive sheet 81 to the chuck surface of the table 24 b.

The press machine 15 tightly closes the vacuum process chamber 20 andopens the exhaust valve 28 d to evacuate the vacuum process chamber 20.After the vacuum process chamber 20 is depressurized to a predeterminedpressure (almost vacuum), the upper surface plate 23 a is lifted down tothe position where the press plate 24 a comes in close contact with theadhesive sheet 81. The exhaust valve 28 d is closed and the gas inletvalve 28 e is opened to set the chamber pressure nearly to theatmospheric pressure. With the vacuum process chamber 20 opened, theupper surface plate 23 a is lifted upward so that the adhesive sheet 81on the table 24 b is separated by the transfer mechanism.

According to the impurity removing method, the adhesive sheet 81 isadhered to the press plate 24 a and table 24 b evenly and firmly invacuum and the impurities 84, such as dust or glass pieces, find theirway into the adhesive layer 83. Therefore, even minute dust iseffectively removed from the chuck surface.

The elasticity of the tape base 82 allows dust or the like to be removedfrom the chuck surfaces of the press plate 24 a and table 24 b withoutdamaging the chuck surfaces.

To enhance the impurity removing effect, it is preferable to execute themethod with the vacuum process chamber 20 depressurized. The method mayhowever be executed in the atmospheric pressure in which case, the timeto depressurize the vacuum process chamber 20 is shortened and a certaindegree of an impurity removing effect is acquired.

Instead of sandwiching the adhesive sheet 81 between the press plate 24a and table 24 b, the adhesive sheet 81 may be adhered to each of thepress plate 24 a and table 24 b and be separated therefrom later. Incase where the adhesive layer 83 is applied only to one side of the tapebase 82, the impurities adhered to the press plate 24 a and table 24 bmay be removed alternately in an arbitrary order or the adhesive sheet81 may be adhered to the press plate 24 a and table 24 b individually.

In a case where the press plate 24 a and table 24 b are detachable fromthe press machine 15, impurities may be removed by the adhesive sheet 81outside the vacuum process chamber 20 (outside the bonded-substratefabricating apparatus 10).

The amount of a liquid crystal to be sealed between the substrates W1and W2 will be discussed below.

Because two substrates W1 and W2 should be bonded together with anextremely small gap (cell thickness), it is necessary to adjust theamount of a liquid crystal to be sealed to the adequate amount.

As shown in FIG. 9, a plurality of spacers or poles 85 for restrictingthe gap (cell thickness) between the substrates W1 and W2 to apredetermined value are formed on one substrate (the array substrate W1on which the liquid crystal is to be dropped in the first embodiment).After a liquid crystal LC is dropped within the frame of a sealingmaterial 86, the substrates W1 and W2 are bonded together.

The height of the poles 85 (pole height) may vary from a predeterminedvalue. The variation in pole height causes the gap between thesubstrates W1 and W2 to change from its predetermined value. It istherefore necessary to adjust the dropping amount of the liquid crystalLC in accordance with the pole height before bonding the substrates W1and W2. The adjustment of the dropping amount of the liquid crystal LCwill be described below referring to FIG. 10.

FIG. 10 shows the bonded-substrate fabricating apparatus 10 which isequipped with a plurality of seal patterning systems 12, a plurality ofliquid crystal dropping devices 13, a plurality of press machines 15 anda plurality of curing devices 16. The ID reader 18 is provided in thefirst transfer equipment 17 a.

A pole height measuring unit 87 is connected to the bonded-substratefabricating apparatus 10 via a network. The pole height measuring unit87 measures the height of the poles 85 formed on one of the substratesW1 and W2 (e.g., the array substrate W1). The measuring unit 87 has anID reader 88 for reading a substrate ID to distinguish the types of thesubstrates W1 and W2.

In step S91 a in FIG. 11A, the ID reader 88 reads the substrate ID ofthe substrate W1. In step S92 a, the pole height measuring unit 87measures the height of the poles 85 formed on the substrate W1. In stepS93 a, the pole height measuring unit 87 stores the measuring result orpole height information in a first memory device 87 a in the pole heightmeasuring unit 87 in association with the substrate ID. The pole heightmeasuring unit 87 performs steps S91 a to S93 a in advance before thesubstrate W1 is transferred to the bonded-substrate fabricatingapparatus 10.

As shown in FIG. 11B, when the first transfer equipment 17 a receivesthe substrates W1 and W2, the control unit 11 (see FIG. 1) causes the IDreader 18 to read the substrate ID of the substrate W1 (step S91 b).Specifically, the first transfer equipment 17 a reads the substrate IDof the substrate W1 having the poles 85 and transfers the substrates W1and W2 to the associated seal patterning system 12 in accordance with aninstruction from the control unit 11.

The control unit 11 reads the pole height information associated withthe substrate ID of the substrate W1 from the first memory device 87 aand stores the pole height information into a second memory device 87 bin the control unit 11 (step S92 b). Based on the pole heightinformation, the control unit 11 determines the liquid crystal droppingdevice 13 that drops the liquid crystal LC (step S93 b). In a case wherethe bonded-substrate fabricating apparatus 10 is provided with only onetype of liquid crystal dropping device 13, step S93 b is omitted and thesecond transfer equipment 17 b transfers the substrates W1 and W2 fromthe seal patterning system 12 to that liquid crystal dropping device 13.

In step S94 b, the control unit 11 computes the dropping amount of theliquid crystal LC. Specifically, a correction value for correcting anerror in the dropping amount of the liquid crystal LC among a pluralityof liquid crystal dropping devices 13 is set beforehand for each liquidcrystal dropping device 13. The control unit 11 computes the properdropping amount of the liquid crystal LC based on the dropping amount ofthe liquid crystal LC for the pole height information acquiredbeforehand through experiments and the correction value for the droppingamount.

The control unit 11 instructs the proper dropping amount of the liquidcrystal LC to the liquid crystal dropping device 13 (step S95 b) and theliquid crystal dropping device 13 drops the proper dropping amount ofthe liquid crystal LC onto the substrate W1 (step S96 b).

According to the control method in FIGS. 11A and 11B, the droppingamount of the liquid crystal LC is corrected in accordance with the poleheight of the poles 85 formed on the substrate W1 and which liquidcrystal dropping device 13 was used. This reduces the rate of defects ofthe integrated substrates W1, W2, thus reducing the wasteful amount ofthe liquid crystal LC in use.

The serial number information of the pole height measuring unit 87 thathas measured the pole height may be added to the substrate ID and thepole height information and stored in the first memory device 87 a.

In some cases, the bonded-substrate fabricating apparatus 10 may have aplurality of pole height measuring units 87 for the purpose of massproduction and stable operation or the like. In such a case, there is apossibility that an error occurs in the measured value of the poleheight due to a variation in the pole height measuring units 87. It istherefore important to grasp which pole height measuring unit 87 hasbeen used to measure the pole height information of the substrate W1.Adding the serial number information of the pole height measuring unit87 to the substrate ID and the pole height information ensurescomputation of the proper dropping amount of the liquid crystal LC inconsideration of variations in the pole height measuring units 87 andthe liquid crystal dropping devices 13.

A lot number may be added to the substrate ID and the pole heightinformation and stored in the first memory device 87 a. The lot numberis a number to be given to a predetermined number of substrates W1 whichare processed in a predetermined process unit period. Since the poleheight information of the substrates W1 that have the same lot numbercan be acquired at a time according to the method, it is possible tocalculate the dropping amount of the liquid crystal on the substrates W1having the same lot number beforehand. This can eliminate the trouble ofcalculating the dropping amount of the liquid crystal for eachsubstrate, so that the response time of the control unit 11 can beshortened and the productivity can be improved.

The first embodiment has the following advantages.

(1) While a gas is injected toward the inner surface of the secondsubstrate W2, the second substrate W2 is transferred to the pressmachine 15 and held on the press plate 24 a by the transfer robot 31which chucks and holds the outer edge area of the inner surface or atransfer robot 31 that chucks and holds the outer edge area of the outersurface of the second substrate W2. Therefore, even the second substrateW2 which is likely to be bent due to the dead load is held on the pressplate 24 a while being kept horizontally. As the second substrate W2 isstably held on the press plate 24 a, the positional deviation of thesecond substrate W2 on the press plate 24 a, the separation of thesecond substrate W2 from the press plate 24 a and the generation of aglow discharge at the time of performing electrostatic chuck areprevented. This results in improvements on the production yield andproductivity of large and thin LCD panels.

(2) As the back pressure of the second substrate W2 is keptapproximately equal to the pressure in the vacuum process chamber 20,local bending of the second substrate W2 originated from the pressuredifferential between the top and bottom surfaces of the second substrateW2 is prevented. Further, the movement or separation of the secondsubstrate W2 is prevented due to bubbles remaining on the contactsurface between the chuck surface of the press plate 24 a and the secondsubstrate W2, during depressurization of the vacuum process chamber 20.

(3) A plurality of grooves 25 a are formed at predetermined pitches inthe chuck surface of the press plate 24 a with the end face (side) ofthe press plate 24 a being cut away. Accordingly, the movement orseparation of the second substrate W2, originated from even if bubblesremain on the contact surface been the press plate 24 a and the secondsubstrate W2, the bubbles become easier to move into the vacuum processchamber 20 during depressurization of the vacuum process chamber 20.Therefore, the movement or separation of the second substrate W2 or thelike originated from the influence (expansion or the like) of thebubbles is prevented too.

(4) The porous member 80 having a permeability is provided in thegrooves 25 a of the press plate 24 a. This structure surely prevents thelocal bending of the second substrate W2 originated from the pressuredifferential between the top and bottom surfaces of the second substrateW2 at the time of sucking the second substrate W2. This advantage canfurther enhance the advantage (2).

(5) Impurities, such as dust or glass pieces, adhered to the press plate24 a and the table 24 b are removed by the adhesive sheet 81. As theadhesive sheet 81 is adhered to the press plate 24 a and table 24 bevenly and firmly in vacuum in the present embodiment, those impuritiesare effectively removed.

(6) The pole height measuring unit 87 measures the height of the poles85 of the substrate W1. The optimal dropping amount of the liquidcrystal LC which is corrected in accordance with the pole heightinformation and the liquid crystal dropping device 13 that drops theliquid crystal LC is dropped on the substrate W1. This can reduce therate of defects of the integrated substrates W1, W2 and the wastefulamount of the liquid crystal LC in use. By adding the serial numberinformation of the pole height measuring unit 87 that has measured thepole height and a lot number to the pole height information, thedropping amount of the liquid crystal LC can be corrected moreaccurately and more efficiently. As the amount of the liquid crystal LCto be sealed is optimized, the yield of the liquid crystal panels isimproved, thus making it possible to cope with products with a narrowsubstrate gap.

The following will discuss a transfer robot 101 and a method offabricating a bonded substrate according to the second embodiment of theinvention. As like or same reference numerals are given to thosecomponents which are the same as the corresponding components of thefirst embodiment that has been described earlier with reference to FIG.2, their detailed descriptions will be partly omitted.

FIG. 12 shows the layout of the bonding device 14 (the curing device 16not illustrated). The transfer robot 101 is provided between thepositioning device 102 which carries out positioning of the firstsubstrate W1 and the second substrate W2, the press machine 15 whichcarries out a bonding work and a disposing position 103 and is swingableto positions that respectively face the positioning device 102, thepress machine 15 and the disposing position 103.

In the first bonding step for the substrates W1 and W2, it is necessaryto transfer three types of parts (first substrate W1, second substrateW2 and integrated substrate W1, W2). To improve the fabricationefficiency of a bonded substrate, an improvement of the transferefficiency for those three types of parts is demanded.

The transfer robot 101 has a rotary portion 104, a first transfer arm105 and a second transfer arm 106. As shown in FIG. 13A, the rotaryportion 104 is provided in such a way as to be rotatable approximately360 degrees about a body 104 a and movable up and down along the axis (Zaxis) of the body 104 a. The first and second transfer arms 105 and 106are individually extensible and contractible horizontally (directions ofthe X axis and Y axis) with respect to the rotary portion 104 and areslightly movable up and down in the Z-axial direction.

Therefore, the transfer robot 101 swings to each of the positions of thepositioning device 102, the press machine 15 and the disposing position103 and extends or contracts at least one of the first and secondtransfer arms 105 and 106 to transfer the substrates W1 and W2.

As shown in FIG. 13B, holding members or first and second hands 105 aand 105 b are provided at the distal end of the first transfer arm 105.A plurality of chuck pads 107 are provided on the bottom surface of thefirst hand 105 a. The chuck pads 107 hold the second substrate W2.Specifically, the chuck pads 107 suck the outer surface of the secondsubstrate W2 by means of an unillustrated vacuum source. A plurality ofchuck pads 108 are provided on the top surface of the second hand 105 b.The plurality of chuck pads 108 suck the outer surface of the firstsubstrate W1.

As shown in FIG. 13C, a holding member or a third hand 106 a is providedat the distal end of the second transfer arm 106. A plurality of chuckpads 109 are provided on the top surface of the third hand 106 a. Thechuck pads 109 suck the integrated substrate W1, W2.

The transfer robot 101 first swings to the position facing thepositioning device 102, holds one of the positioned substrates (secondsubstrate W2) with the first hand 105 a and takes out the substrate W2from the positioning device 102. Next, the transfer robot 101 holds theother positioned substrate (first substrate W1) with the second hand 105b and takes out the substrate W1 from the positioning device 102. Thosemanipulations are carried out while the press machine 15 is bonding theprevious substrates W1 and W2.

Next, the transfer robot 101 swings to the position facing the pressmachine 15. When the press machine 15 completes bonding the previoussubstrates W1 and W2, the transfer robot 101 holds the integratedsubstrate W1, W2 with the third hand 106 a and takes out the integratedsubstrate W1, W2 from the press machine 15. Subsequently, the transferrobot 101 transfers the substrates W2 and W1, respectively held by thefirst and second hands 105 a and 105 b, to the press machine 15.

Thereafter, the transfer robot 101 swings to the position facing thedisposing position 103 and disposes the integrated substrate W1, W2 heldby the third hand 106 a in the disposing position 103.

As apparent from the above, the transfer robot 101 performs a swingoperation from the positioning device 102 to the disposing position 103,a single extensible and contractible operation of the first transfer arm105 to transfer a set of substrates W1 and W2 to the press machine 15and a single extensible and contractible operation of the secondtransfer arm 106 to transfer the integrated substrate W1, W2 from thepress machine 15. That is, the transfer robot 101 can transfer a set ofsubstrates W1 and W2 by a single swing operation and two extensible andcontractible operations.

By way of contrast, the first transfer arm of the conventional transferrobot has the first hand (singular) and the second transfer arm has thesecond hand (singular). Therefore, the conventional transfer robot needsto perform two swing operations from the positioning device 102 and atotal of three extensible and contractible operations of the first andsecond transfer arms for carrying the substrates W1 and W2 into/out ofthe press machine 15 at the time of executing a single transfer of thesubstrates W1 and W2 to the press machine 15. Because the use of thetransfer robot 101 in FIG. 13A reduces the number of operations, thetransfer time of substrates is shortened, which can thus shorten thetime in which the operation of the press machine 15 is stopped. Thetransfer robot 101 therefore ensures an efficient transfer work.

In a case where the second substrate W2 is carried into the pressmachine 15 by the first hand 105 a (to be held on the press plate 24 a),it is preferable to use a press plate 111 shown in FIGS. 15A and 15B.The press plate 111 has a channel 111 a formed along the moving passageof the first hand 105 a. The first hand 105 a moves under the pressplate 111 while holding the outer surface of the second substrate W2 andmoves upward to a position where the second substrate W2 comes close tothe chuck surface of the press plate 111 as shown in FIGS. 15A and 15B.As the first hand 105 a is retained in the channel 111 a at that time,it does not interfere with the press plate 111. In this state, the pressplate 111 chucks and holds the second substrate W2 by at least one ofsuction and electrostatic force. After suction of the second substrateW2 is stopped, the first hand 105 a moves upward to be away from thesecond substrate W2. Finally, the first transfer arm 105 is pulled back.

Because the first hand 105 a sucks and holds the outer surface of thesecond substrate W2, weight-originated bending of the second substrateW2 is prevented even if the second substrate W2 is large and thin. Thesecond substrate W2 is therefore chucked to the chuck surface of thepress plate 111 in an approximately flat state.

At least one of the first and second transfer arms 105 and 106 of thetransfer robot 101 is provided with two hands. Accordingly, the secondtransfer arm 106 may have two hands.

The first hand 105 a may be replaced with the hand 31 a in FIG. 2. Inthis case, for example, the hand 31 a which transfers the secondsubstrate W2 is provided at the first transfer arm 105 and the secondhand 105 b which transfers the substrate W1 and the third hand 106 awhich transfers the integrated substrate W1, W2 are provided at thesecond transfer arm 106.

The positioning device 102 will be discussed below.

In case of bonding the substrates W1 and W2, the substrates W1 and W2should be aligned at a high precision (within an error of severalmicrometers). In this respect, alignment marks of a size of microns areformed on the substrates W1 and W2. Normally, a lens with a long focaldistance is needed to simultaneously catch the alignment marks of thetwo apart substrates W1 and W2. Such a lens is however complex instructure and expensive. It is therefore preferable that the positioningdevice 102 should perform preliminary positioning of the substrates W1and W2 before the press machine 15 would bond the substrates W1 and W2.

As shown in FIG. 14, the positioning device 102 has a base plate 121,positioning pins 122 attached to the base plate 121, support plates 123for supporting the second substrate W2, a support pin 124 which supportsthe substrate W1, a chuck mechanism 125, a positioning mechanism 126 anda linear actuator 127.

The support plates 123 are movable to a position for supporting theouter edge area of the inner surface of the second substrate W2 and aposition apart from the second substrate W2 along linear guides 121 aprovided on the base plate 121. The support pin 124 is movable up anddown. The positioning mechanism 126 is movable as indicated by arrows inFIG. 14A. The driving of the support plates 123, the support pin 124 andthe positioning mechanism 126 is controlled by a drive source, such asunillustrated cylinders or the like.

The chuck mechanism 125 is supported by the linear actuator 127 in sucha way as to be movable up and down with respect to the base plate 121.The chuck mechanism 125 has an upper plate 128 a, a lower plate 128 b, abearing 129 which supports the upper plate 128 a in such a way that theupper plate 128 a is movable horizontally in the directions of the Xaxis and Y axis with respect to the lower plate 128 b, and a spring 130which urges the upper plate 128 a to a reference position (the positionshown in FIG. 14A) of the lower plate 128 b. A plurality of chuckportions 131 are provided on the bottom surface of the upper plate 128 ain parallel at predetermined pitches. Each chuck portion 131 has a chuckpad 132.

The positioning of the substrates W1 and W2 will be discussed below.

First, the second substrate W2 is positioned as follows. The chuckmechanism 125 is moved upward and the support pin 124 is moved downward.The third transfer equipment 17 c (see FIG. 1) transfers the secondsubstrate W2 to the positioning device 102 from the liquid crystaldropping device 13. As a result, the second substrate W2 is supported onthe support plates 123 as indicated by a two-dot chain line in FIG. 14A.

As the second substrate W2 is placed on the support plates 123, thechuck mechanism 125 is moved downward and sucks and holds the topsurface (outer surface) of the second substrate W2 by means of the chuckpads 132. The chuck mechanism 125 is moved upward together with thesecond substrate W2 and the support plates 123 are moved to positionswhere the support plates 123 do not interfere with the second substrateW2. The second substrate W2 is suspended from the chuck mechanism 125.

Next, the positioning mechanism 126 moves forward to move the secondsubstrate W2 horizontally toward the positioning pins 122 provideddiagonal to the positioning mechanism 126. The positioning mechanism 126pushes the edge (the corner or the side near the corner) of the secondsubstrate W2 until a predetermined position or until the corner of thesecond substrate W2 abuts on the positioning pins 122. At that time, thechuck mechanism 125 which is holding the second substrate W2 moves too.The movements of the chuck mechanism 125 and the second substrate W2 arecarried out smoothly by the bearing 129.

The transfer robot 101 extends the first transfer arm 105. The firsthand 105 a sucks and holds the top surface of the second substrate W2placed in a predetermined position. When the transfer robot 101 holdsthe second substrate W2, the chuck mechanism 125 stops sucking thesecond substrate W2. After chucking of the second substrate W2 isstopped, the chuck mechanism 125 is moved upward by the linear actuator127 and is returned to the reference position by the urging force of thespring 130.

Next, the third transfer equipment 17 c (see FIG. 1) transfers thesubstrate W1 to the positioning device 102 from the liquid crystaldropping device 13. Before the transfer, the chuck mechanism 125 shouldhave been moved upward and the support plates 123 should have been movedto positions where the support plates 123 do not interfere with thesubstrate W1. The substrate W1 is supported by the lifted-up support pin124. The positioning mechanism 126 pushes the edge of the substrate W1to move the substrate W1 to a predetermined position. The transfer robot101 extends the first transfer arm 105 and sucks and holds the bottomsurface of the substrate W1 by means of the second hand 105 b.

According to the positioning device 102, the second substrate W2 ischucked by the chuck mechanism 125 having the chuck pads 132, so thatbending of the second substrate W2 due to its dead load is suppressedand the second substrate W2 is positioned in an approximately flat stateby the positioning mechanism 126.

By way of contrast, the conventional positioning device does not havethe chuck mechanism 125. In a case where the second substrate W2 islarge or thin, therefore, the second substrate W2 bends. Thus, when thebent substrate is positioned, the bending of the second substrate W2becomes greater, so that accurate positioning cannot be ensured,disadvantageously.

According to the second embodiment, the second substrate W2 ispositioned in an approximately flat state, thus improving the precisionof positioning the second substrate W2. This results in an improvementon the alignment precision in the press machine 15.

The second embodiment has the following advantages in addition to theadvantages (1) to (6).

(7) The transfer robot 101 includes the first transfer arm 105 havingthe first and second hands 105 a and 105 b and the second transfer arm106 having the third hand 106 a. As the transfer robot 101 can carry twosubstrates W1 and W2 into the press machine 15 at a time, the number ofthe swing operations and extensible and contractible operations of thetransfer robot 101 is reduced and the transfer time is shortened. Thismakes it possible to shorten the transfer-oriented idling time of thepress machine 15, thus improving the productivity of the bondedsubstrate.

(8) The first and second hands 105 a and 105 b suck and hold the outersurfaces of the substrates W2 and W1. This allows even large and thinsubstrates W2 and W1 to be stably held in an approximately flat statewithout being bent. Because the first and second hands 105 a and 105 bcan be attached to the first transfer arm 105 at relatively narrowpitches, enlargement of the press machine 15 can be avoided.

(9) Because the positioning device 102

positions the second substrate W2 held on the chuck mechanism 125 in anapproximately flat state, the positioning precision is improved. Thisresults in an improved positioning precision in the press machine 15. Asthe positioning device 102 can position the second substrate W2 quickly,the alignment time in the press machine 15 is shortened, thus shorteningthe fabrication time for bonded substrates.

(10) As the first and second hands 105 a and 105 b do not contact theinner surfaces of the substrates W2 and W1, changes in the properties ofthe inner surfaces of the substrates W2 and W1 are prevented.

A description will now be given of a press machine 141 and a bondingmethod according to the third embodiment of the invention. As like orsame reference numerals are given to those components which are the sameas the corresponding components of the first embodiment that has beendescribed earlier with reference to FIG. 2, some of their detaileddescriptions will not be repeated.

As shown in FIG. 16, the press machine 141 has a first exhaust valve 28d for evacuating the vacuum process chamber 20, a bypass pipe 26 f whichconnects the main pipe 26 a to the depressurizing pipe 26 d, and asecond exhaust valve 28 f which is provided in the bypass pipe 26 f andevacuates the main pipe 26 a and vacuum line 25. The opening/closingaction of the second exhaust valve 28 f is controlled by theunillustrated control unit.

In a case where the press machine 141 is used, steps S151 to S153 inFIG. 17 are executed in place of step S48 in FIG. 5 and step S70 in FIG.6. That is, in step S151, the press machine 141 opens the first andsecond exhaust valves 28 d and 28 f and opens the gas inlet valve 28 eand starts gas substitution in the vacuum process chamber 20.

At the beginning of the depressurization of the vacuum process chamber20, the exhaust valves 28 d and 28 f are opened relatively narrowly sothat a variation in pressure does not become too large. A variation inpressure may be adjusted by increasing the rotational speed of thevacuum pump 29 gradually.

In step S152, the press machine 141 gradually increases the degrees ofopening of the first and second exhaust valves 28 d and 28 f in such away that the back pressure of the second substrate W2 becomesapproximately equal to or lower than the chamber pressure. When thechamber pressure and the back pressure of the second substrate W2 reachpredetermined values, the press machine 141 fully opens both exhaustvalves 28 d and 28 f (step S153).

The subsequent steps are the same as those of the first embodiment. Thatis, after the gas substitution in the vacuum process chamber 20 iscompleted, the gas inlet valve 28 e is closed and the substrates W1 andW2 are aligned and pressed.

According to the third embodiment, the degrees of opening of the exhaustvalves 28 d and 28 f (the exhaust speed and depressurizing speed) areadjusted, so that even when the conductance from the chuck surface ofthe press plate 24 a to the vacuum process chamber 20 (the degrees ofvacuum in the vacuum line 25 and the pipes 26 a and 26 b) is relativelysmall, it is possible to adjust the back pressure of the secondsubstrate W2 to be approximately equal to or lower than the chamberpressure. In other words, even when the passage from the chuck surfaceof the press plate 24 a to the vacuum process chamber 20 is narrow anddepressurization is difficult, advantages similar to those of the firstembodiment can be acquired. Note that the third embodiment brings aboutsimilar advantages even without the pipe 26 b and the back pressurerelease valve 28 b.

A fabrication apparatus and method for bonded substrates according tothe fourth embodiment of the invention will be discussed below.

FIG. 18A shows an upper holding plate 161 according to the fourthembodiment. The upper holding plate 161 includes an upper surface plate162 and a press plate 163. Through passages 164 are formed in such a wayas to extend from the chuck surface of the press plate 163 to the topsurface of the upper surface plate 162.

The upper holding plate 161 includes a chuck mechanism 165 which issupported by an unillustrated drive mechanism in such a way as to bemovable up and down. The chuck mechanism 165 comprises a top plate 165a, chuck portions 165 b supported on the top plate 165 a and chuck pads165 c provided at the distal ends (lower ends) of the individual chuckportions 165 b. The chuck portions 165 b are respectively inserted intothe through passages 164. The chuck pads 165 c are connected to a vacuumsource via an unillustrated passage. The suction force from the vacuumsource allows the outer surface of the second substrate W2 to be suckedto the chuck portions 165 b.

As shown in FIG. 18A, the chuck mechanism 165 is lifted downward in sucha way that the chuck pads 165 c are placed below the chuck surface ofthe press plate 163. The second substrate W2 held by the transfer robot31 (FIG. 2) is chucked to the chuck pads 165 c.

The chuck mechanism 165 is lifted upward to a position where the secondsubstrate W2 comes close to the chuck surface of the press plate 163. Asthe suction force or electrostatic force is allowed to act on the secondsubstrate W2 in that state, the second substrate W2 is sucked to thepress plate 163 and the chucking work of the chuck mechanism 165 isstopped. As a result, the second substrate W2 is held on the press plate163 (FIG. 18B).

According to the fourth embodiment, the second substrate W2 is held onthe press plate 163 while being sucked by the chuck portions 165 b.Therefore, the second substrate W2 even bent greatly is held on thepress plate 163 in an approximately flat state, thus preventingpositional deviation and separation of the second substrate W2.

As shown in FIG. 18B, the pressure in the vacuum process chamber 20 actson the top surface of the second substrate W2 via the through passages164. During depressurization of the vacuum process chamber 20,therefore, the back pressure of the second substrate W2 does not becomehigher than the chamber pressure, thus preventing separation of thesecond substrate W2.

The chuck portions 165 b may be moved up and down individually andindependently. In this case, a substrate which is bent greatly ischucked smoothly.

It should be apparent to those skilled in the art that the presentinvention may be embodied in many other specific forms without departingfrom the spirit or scope of the invention.

Although the transfer of the substrate W2 has been described in thedescription of the first embodiment, the lower substrate W1 may likewisebe transferred while a gas is injected toward the bottom surface of thelower substrate W1.

In the bonding method in FIG. 5, step S44 (tight closing of the vacuumprocess chamber 20) may be executed after step S47.

The transfer robot 31 may spout a gas other than an inactive gas towardthe bottom surface of the second substrate W2.

A filter may be provided upstream of the gas injection nozzle 34 so thatdust does not stick to the second substrate W2.

The transfer robot 31 may be modified in such a way as to have amechanism which chucks the top surface of the second substrate W2 whilespouting a gas to the bottom surface of the second substrate W2 in acase where the second substrate W2 is large.

The first memory device 87 a and the second memory device 87 b whichstore the substrate ID and pole height information may be provided in aserver connected to the bonded-substrate fabricating apparatus 10 via anetwork.

The parts that are respectively held by the first to third hands 105 a,105 b and 106 a are not limited to those types which have been discussedin the foregoing descriptions of the embodiments. To describe in detail,the substrate W1 may be held and transferred by the third hand 106 a,and the integrated substrate W1, W2 may be held and carried out of thepress machine 15 by the second hand 105 b. In case where the substratesW2 and W1 are respectively held by the first and second hands 105 a and105 b of the first transfer arm 105 as described in the descriptions ofthe embodiments, dust is prevented from falling on the surface of thesubstrate W1.

Therefore, the present examples and embodiments are to be considered asillustrative and not restrictive and the invention is not to be limitedto the details given herein, but may be modified within the scope andequivalence of the appended claims.

1. A method of bonding two substrates held by first and second holdingplates arranged to face each other in a process chamber, the methodcomprising: vacuum holding at least one of the two substrates by atleast one of the first or second holding plates in the process chamber;feeding a gas in the process chamber to elevate pressure in the processchamber to a predetermined elevated pressure higher than the atmosphericpressure; electrostatically holding said at least one of the twosubstrates by said at least one of the first or second holding platesafter the pressure in the process chamber is elevated to thepredetermined elevated pressure, pressing the two substrates to bond toeach other after said electrostatically holding said at least one of thetwo substrates; and stopping the vacuum holding before pressing the twosubstrates.
 2. The method of bonding two substrates according to claim1, wherein said stopping is performed when the pressure in the processchamber is higher than the atmospheric pressure.
 3. The method ofbonding two substrates according to claim 1, further comprisingevacuating the process chamber before pressing the two substrates andafter electrostatically holding said at least one of the two substrates.4. The method of bonding two substrates according to claim 1, furthercomprising: evacuating the process chamber before said pressing the twosubstrates and after both of said electrostatically holding said atleast one of the two substrates and said stopping the vacuum holding.